In recent years, demand for liquid crystal displays (LCDs), in particular color liquid crystal displays, has been increasing in accordance with development in personal computers and large-sized liquid crystal TVs. There is also an expectation for organic EL displays to become common due to the desire for improved image quality. There has also been a remarkable growth in demand for solid-state image sensors, such as CCD image sensors, as digital cameras and camera-equipped cellular phones become popular.
A color filter is a key device used in these displays or optical elements, and reduction in costs for producing color filters has been desired in addition to the improvement in image quality. Typically, a color filter includes color patterns of three primary colors, red (R), green (G) and blue (B), and these color patterns separate light passing through a display device or an image sensor into three primary colors.
Dyes used for color filters generally need to satisfy the following requirements.
Specifically, the dyes need to: have favorable spectral characteristics in terms of color reproduction; not exhibit optical disorders such as uneven optical density that may cause light scattering that lowers the contrast of liquid crystal displays, or color unevenness/roughness of solid-state image sensors; exhibit robustness against environmental conditions under which the devices are used, such as favorable heat fastness, light fastness and moisture fastness; have a large molar absorbance coefficient that enables formation of a thin film; and the like.
In the production of color filters, a pigment dispersion method has been used. Color filters produced from a colored curable composition in which a pigment is dispersed in a curable composition by photolithography or inkjetting, the colored curable composition being prepared by a pigment dispersion method, are stable with respect to light or heat due to the use of a pigment.
In the process of photolithography, colored pixels are formed by applying a radiation-sensitive composition onto a support with a spin coater, a roll coater or the like, drying the coated film, and subjecting the dried coated film to pattern exposure and development. A color filter can be obtained by repeating these processes for a number of times corresponding to the number of colors used in the color filter. Since light is used to form a pattern in photolithography, whereby positional accuracy of the obtained pattern is excellent, photolithography has been widely used as a method suitable for producing large-sized, high-resolution color filters. In recent years, photolithography has been particularly advantageous for producing solid-state image sensors that require a further increase in resolution.
As mentioned above, a further increase in the resolution of color filters for solid-state image sensors has been desired in recent years.
However, in a conventional pigment dispersion method, it has been difficult to further improve the resolution due to color unevenness caused by coarse pigment particles, or the like. Therefore, in a field in which a fine pattern is required, such as solid-state image sensors, performing photolithography in which a pigment dispersion method is employed is becoming difficult. On the other hand, in the field of liquid crystal displays, color filters produced by photolithography in which a pigment dispersion method is employed have problems such as a reduced contrast due to light scattering caused by pigment particles or an increased amount of haze, although these color filters exhibit excellent light fastness and heat fastness.
In addition to photolithography, a method in which colored layers (color pixels) are formed by discharging color ink by inkjetting has been proposed as a method of producing a color filter (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 59-75205 and 2004-339332).
An inkjet method is a method of recording characters or images by applying ink directly onto a recording medium by jetting ink droplets from fine nozzles. An inkjet method, in which inkjet heads are sequentially moved, has an advantage in that a large-sized color filter can be produced at high productivity and favorable operability while generating low noise. In the production of color filters by an inkjet method, inkjet inks prepared by a pigment dispersion method are used. As inkjet inks prepared by a pigment dispersion method, for example, an inkjet ink for producing a color filter, which ink includes a binder component, a pigment and a solvent having a boiling point of 180° C. to 260° C. and a vapor pressure of 0.5 mmHg or less at room temperature, has been proposed (see for example, JP-A No. 2002-201387).
When inkjet inks prepared by a pigment dispersion method are used to produce a color filter, since nozzle clogging frequently occurs due to coagulation of a pigment, there has been a demand for improving discharge stability. In addition, recoverability of the state of ink discharge by a recovery operation such as wiping or purging tends to decrease. Further, there may be a case in which ink discharge deviates from the right direction as a result of performing wiping during which nozzle surfaces are scraped with the coagulated pigment.
When a dye is used instead of a pigment, an increase in resolution can be expected as a result of overcoming the problems of color unevenness/roughness in the case of color filters for solid-state image sensors; and improvement in optical properties in terms of contrast or haze can be expected in the case of color filters for liquid crystal displays or organic EL displays. In addition, in an inkjet method in which a dye is used, discharge stability is generally favorable, and the state of ink discharge can be readily recovered by performing wiping or purging even if nozzle clogging is caused cue to the increased viscosity of the ink.
Under such circumstances, use of a dye as a dye has been taken into consideration (for example, see JP-A No. 6-75375). However, a curable composition containing a dye has newly raised the following problems.
(1) Dyes generally exhibit inferior light fastness and heat fastness compared with pigments. In particular, optical properties of dyes may change due to high temperature during sputtering of ITO (indium tin oxide) that are commonly used as an electrode for liquid crystal displays (LCDs) or flat panel displays (FPDs).
(2) Since dyes tend to suppress radical polymerization reaction, design of a colored curable composition becomes difficult in a system in which radical polymerization is used as a means of curing.
(3) Since ordinary dyes have a low solubility in an alkali aqueous solution or an organic solvent (hereinafter, also simply referred to as a solvent), it is difficult to obtain a curable composition having a desired spectrum.
(4) Since dyes often interact with other components in a colored curable composition, it is difficult to adjust the solubility of a cured portion or an uncured portion (developability).
(5) When dyes have a low molar absorbance coefficient (ε), a large amount of dye needs to be added and the amount of other components in the colored curable composition, such as a polymerizable compound (monomer), a binder, a photopolymerization initiator or the like, needs to be reduced. As a result, curability of the composition, heat fastness after curing, or developability of a cured or uncured portion, may decrease.
Due to these problems, it has been difficult to use a dye to form a colored pattern for color filters that exhibits a high resolution, an excellent ability of forming a thin film, and an excellent robustness.
In addition, since color filters for solid-state image sensors need to be formed into a thin film (for example, to a thickness of 1 μm or less), a large amount of dye need to be added in a curable composition, thereby exaggerating the problems as mentioned above.
With regard to such problems, various methods of selecting the type of initiator or increasing the amount of the initiator have been proposed (for example, see JP-A No. 2005-316012).
A method of producing a color filter has been proposed in which a colored pattern after being formed on a support is exposed to light while heating the support in order to cause polymerization while increasing the exposure temperature to increase the polymerization ratio in the system (see, for example, Japanese Patent No. 3309514).
A method of producing a color filter has been proposed in which a color filter is exposed to light between the development and the heat treatment, thereby suppressing deformation of the color filter (see, for example, JP-A No. 2006-258916).
A colored curable composition and a dye compound using a dipyrromethene dye have been studied in view of its spectral properties suitable for color filters (see for example, JP-A No. 2008-292970).
A color filter including a polymer having a triphenylmethane dye in its molecule as a dye has been proposed in view of overcoming the shortcomings in sublimation during production of color filters (see, for example, Japanese Patent No. 3736221).
In addition to the problems as described above, dye-containing colored compositions for color filters have the following problems that are unique to dyes.
(6) Penetration of dye during application of different color
When a colored pattern is formed from a colored composition using a dye, the dye tends to penetrate into a pattern (or a layer) of a different color that has been previously formed, thereby causing color mixing.
(7) Elution of dye during alkali development
In a colored composition using a dye, a large amount of dye needs to be added and, as a result, the amount of a component that contributes to photolithographic properties is relatively decreased. As a result, sensitivity of the colored composition is lowered and a pattern tends to exfoliate in a region exposed to a low amount of light. In addition, defective formation of a pattern, such as failure to obtain a desired shape or a color density of the pattern due to elution of a dye during alkali development, tends to occur.
(8) Heat diffusion (color transfer) due to heat treatment
In a colored composition using a dye, color transfer tends to occur between the adjacent pixels or between the adjacent layers when a heat treatment is performed after the film formation. The color transfer may cause color mixing.
In addition to the above problems, there is a further problem as described below.
(9) Development residues after development (development residues remaining on support or layer of different color)
Development residues may remain on a support or on a pattern (or a layer) of a different color that has been previously formed. In either case, the development residue may cause color mixing.
Among the problems (6) to (9), in particular, problems (6), (8) and (9) tend to become a cause of color mixing, which may significantly inhibit the improvement in sensitivity, which has been desired in solid-state image sensors in recent years.
JP-A No. 2008-292970 discloses the spectral characteristics originated from the light absorption properties that are unique to dipyrromethene dyes. However, JP-A No. 2008-292970 does not mention the problems such as elution of a dye during alkali development, penetration of a dye, heat diffusion (color transfer) of a dye due to heat treatment, or remaining development residues.
Japanese Patent No. 3736221 discloses the effect of suppressing sublimation derived from the characteristics of a polymer including a triphenylmethane dye. However, Japanese Patent No. 3736221 does not mention the problems such as elution of a dye during alkali development, penetration of a dye, heat diffusion (color transfer) of a dye due to heat treatment, or formation of development residues.
The invention has been made in view of such circumstances, and aims to achieve the following objects.
Specifically, the invention aims to provide a colored composition that can form a colored film in which elution of a dye during alkali development is suppressed, penetration of a dye is suppressed, heat diffusion (color transfer) of a dye due to heat treatment is suppressed, and formation of development residues is suppressed.
The invention also aims to provide an inkjet ink capable of forming colored pixels that exhibit excellent heat fastness and excellent discharge stability.
Further, the invention aims to provide a color filter in which penetration of a dye is suppressed, heat diffusion (color transfer) of a dye due to heat treatment is suppressed, and color mixing due to development residues is suppressed, the color filter exhibiting excellent heat fastness; a method of producing the color filter; a solid-state image sensor having the color filter; and a display device.
The present inventors have made studies on dipyrromethene dye compounds and, as a result, found that when a dye is made into a multimer having at least a specific molecular weight, problems such as penetration of a dye into a layer of a different color, elution of a dye during alkali development, heat diffusion (color transfer) due to heat treatment, and development residues remaining after the development can be suppressed.
Further, the present inventors have found that when a dye is adjusted so as to have a specific molecular weight distribution (dispersity), in addition to a specific molecular weight, problems such as penetration of a dye into a layer of a different color, elution of a dye during alkali development, heat diffusion (color transfer) due to heat treatment, and development residues remaining after the development can be remarkably suppressed.
Moreover, the inventors have found that similar effects can be achieved when the molecular weight and the dispersity of other types of dye compounds are adjusted to be within the same specific ranges.
Although JP-A No. 2008-292970 discloses a dye multimer (a polymer having a triphenylmethane dye in its molecule), the problems addressed by the invention are not mentioned. Accordingly, it is not possible to find a solution to these problems as mentioned above, from the teachings of JP-A No. 2008-292970.
The following are the specific embodiments for solving the problems addressed by the invention. However, the invention is not limited to these specific embodiments.
<1> A colored composition comprising a dye multimer having an alkali-soluble group as a dye, the dye multimer having a weight-average molecular weight (Mw) of from 5,000 to 20,000 and a dispersity (weight-average molecular weight (Mw)/number-average molecular weight (Mn)) of from 1.00 to 2.50.
<2> The colored composition according to <1>, further comprising a polymerizable compound, a polymerization initiator and a solvent.
<3> The colored composition according to <1> or <2>, wherein the dye multimer has an acid value of from 0.5 mmol/g to 3.0 mmol/g.
<4> The colored composition according to any one of <1> to <3>, wherein the dye multimer comprises at least one of structural units represented by following formula (A), formula (B) or formula (C), or is a dye multimer represented by following formula (D):

wherein, in the formula (A), XA1 represents a linking group formed by polymerization; LA1 represents a single bond or a divalent linking group; Dye represents a dye residue obtained by removing any one or more hydrogen atoms in a number of from 1 hydrogen atom to (1+m) hydrogen atoms from a dye compound; XA2 represents a linking group formed by polymerization; LA2 represents a single bond or a divalent linking group; m represents an integer from 0 to 3; and Dye and LA2 may be linked to each other by any one of covalent bonding, ionic bonding or coordinate bonding;

wherein, in the formula (B), XB1 represents a linking group formed by polymerization; LB1 represents a single bond or a divalent linking group; A represents a group capable of being bonded to Dye by ionic bonding or coordinate bonding; Dye represents a dye compound having a group capable of being bonded to A by ionic bonding or coordinate bonding, or a dye residue obtained by removing any one or more hydrogen atoms in a number of from 1 hydrogen atom to m hydrogen atoms from the dye compound; XB2 represents a linking group formed by polymerization; LB2 represents a single bond or a divalent linking group; m represents an integer from 0 to 3; and Dye and LB2 may be linked to each other by any one of covalent bonding, ionic bonding or coordinate bonding;

wherein, in the formula (C), LC1 represents a single bond or a divalent linking group; and Dye represents a dye residue obtained by removing any two hydrogen atoms from a dye compound;

wherein, in the formula (D), LD1 represents an m-valent linking group; m represents an integer from 2 to 100; and Dye represents a dye residue obtained by removing any one hydrogen atom from a dye compound.
<5> A color filter formed from the colored composition according to any one of <1> to <4>.
<6> An inkjet ink comprising the colored composition according to any one of <1> to <4>.
<7> A method of producing a color filter, the method comprising:
applying the colored composition according to any one of <1> to <4> onto a support to form a colored layer;
exposing the colored layer to light via a mask; and
developing the exposed colored layer to form a colored pattern.
<8> A method of producing a color filter, the method comprising:
providing a support having depressed portions defined by partitions; and
applying droplets of the inkjet ink according to <6> to the depressed portions by inkjetting, thereby forming colored pixels of the color filter.
<9> A solid-state image sensor comprising the color filter according to <5>.
<10> A display device comprising the color filter according to <5>.